1. Field of the Invention
This invention relates to a method for the production of a novel dispersion containing minute polymer beads possessing a thermosensitive characteristic. More particularly, this invention relates to a method for the production of a dispersion containing minute polymer beads possessing a thermosensitive characteristic and useful as a raw material for diagnostic microbeads, hydrogels for delivery of drugs, adsorbents for non-ionic surfactants, and cosmetics.
2. Description of the Prior Art
For the production of submicron gel beads possessing a thermosensitive characteristic, a method employing reversed-phase suspension polymerization of a composition of solvent-surfactant-aqueous pregel solution has been disclosed [Yoshiharu Hirose, Takayuki Amiya, Yoshitsugu Hirokawa, and Toyoichi Tanaka, "Material for the First Polymer Gel Forum", 39 (1989)]. This method uses n-hexane as the solvent and sorbitan monolaurate as the surfactant. Aqueous solutions of N-isopropyl acrylamide, N-acryloyloxysuccinimide, N,N'-methylenebisacrylamide (a cross-linking monomer), and ammonium persulfate are usable as the aqueous pregel solution. The disclosed method comprises dissolving sorbitan monolaurate in n-hexane under a nitrogen atmosphere, injecting into the resultant solution an initiator-containing aqueous pregel solution, stirring the resultant mixture, and thereafter polymerizing the stirred mixture in the presence of a small amount of tetramethylene diamine. The hydrodynamic diameter of the beads in the resultant product obtained by this method is about 800 nm while the beads are in a swelled state and about 200 to 300 nm while they are in a contracted state.
Ultramicrospheres exhibiting no thermosensitivity and possessing diameters on the nanometer order and colloids thereof are also producible. Dendrimers [D. A. Tomalia, et al.: Macromolecules, 19, 2466 (1986)], monomolecular microspheres [J. Kumaki: Macromolecules, 19, 2258 (1986)], etc. are examples. These particulate products require a complicated process for synthesis, do not allow easy isolation, and are not capable of regulating particle size by varying temperature.
Minute beads possessing smaller diameters than the aforementioned submicron beads and exhibiting a thermosensitive characteristic, specifically a dispersion containing such minute beads, have been increasingly desired as a raw material for diagnostic microbeads, hydrogels for delivery of drugs, adsorbents for non-ionic surfactants, and cosmetics.
An object of this invention, therefore, is to provide a method which allows the production of a dispersion containing these minute beads.